Check out the video below to see how much voltage you can get from just four diodes.
Step 1: Silicon Diode
A silicon diode is a two-lead semiconductor that gates current flow in one direction. The symbol below shows how a diode is lined up with the schematic symbol. The image was taken from http://www.gadgetjq.com/single_fire_tach_adapter_diode.jpg for copyright purposes. Diodes are used in circuits that convert AC voltages to DC voltages, and also as voltage regulators, clamps, and multipliers.
Current flows in the direction of the arrow. A few other terms of technical use are:
Forward-biased is when the anode is more positive than the cathode, and reverse-bias is the opposite: the anode is made more negative in voltage than the cathode.
There are different kinds of diodes, too. Pin diodes, germanium diodes, schottky diodes, rectifier diodes (p-n junction diodes) name most of them. In this instructable we're going to work with silicon-based pin diodes, although if you're really curious I'd encourage you trying the different kinds of diodes to see how it all shakes out.
Diodes are pretty cheap. You can pick up a pack of 50 from Radio Shack for around $3.
Step 2: Test It for Yourself
Go ahead and dig out a few diodes from your tacklebox, toolbox, bead drawer, or whatever you keep all your electronic goodies in and put them in parallel. Connect your voltmeter to either side and take a reading in ambient light. I get about 4-5mV in ambient light.
Next, grab your maglight and while still taking a reading shine a focused beam on the diodes and see what your voltmeter says. In my configuration using the diodes I had at hand, I was able to get more than 100mV from four diodes. That's not too shabby, especially if you're shuffling that voltage off to a capacitor to either save for later or to build up a larger charge to do something more useful, like light an LED (yeah, like that's more useful) or run your garbage disposal.
You don't have to worry too much about which direction the strip is facing as long as you face the strips all in the same direction.
Step 3: Get Funky
So you're generating voltage with your flashlight and a handful of diodes.....wow. So what's next? That's up to you. You could cover a PCB with them and see how surface area corresponds to voltage, when you get diminishing returns, what the optimum diode to voltage ratio is, etc. You could add in capacitors....throw in an op amp or even a charge pump and turn mV into V.
I dropped $5 at R.S. and got two packs of 50 diodes and etched a PCB. Your designs are endless.
Step 4: Final Thoughts
I hope I was able to share something new with you and that you now have a new-found love for green energy. Don't get to crazy though; a rooftop of diodes will get you in trouble with your significant other.
SympanS made it!